Method and apparatus for encoding/decoding images to minimize redundancy of intra-prediction mode

ABSTRACT

A video encoding apparatus encodes intra-prediction mode information of the current block by excluding information on overlapping or unnecessary intra-prediction modes from a candidate mode group and/or based on whether predicted values of intra-prediction modes of at least a preset number of subblocks are matched with actual intra-prediction modes.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is the US national phase of International PatentApplication No. PCT/KR2011/009080, filed Nov. 25, 2011, which claimspriority to Korean Patent Application No. 10-2010-0119759, filed on Nov.29, 2010 and Korean Patent Application No. 10-2011-0023490, filed onMar. 16, 2011. The above-listed applications are hereby incorporated byreference herein in their entirety.

TECHNICAL FIELD

The present disclosure in one or more embodiments relates to a methodand an apparatus for encoding/decoding video in an intra-predictionmode.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

Due to enormous data sizes, videos require a compressing process beforestorage or transmission. Typical encoding of the video data is performedby intra-predicting or inter-predicting, transforming, quantizing, andentropy-coding each picture of the video data in units of blocks.Particularly, the intra-prediction is performed to reduce redundancy ofdata in the video, and the redundancy of the data is reduced through theintra-prediction which performs the prediction from neighboring blocksby using spatial redundancy. At this time, the inventor(s) has/havenoted that the compression capability may deteriorate due to unnecessaryinformation or overlapping information included in intra-prediction modeinformation.

SUMMARY

Some embodiments of the present disclosure provide a video encodingapparatus including an intra-prediction encoder and a prediction modeencoder. The intra-prediction encoder is configured to encode a currentblock by intra-predicting the current block by using pixels ofneighboring blocks adjacent to the current block. The prediction modeencoder is configured to encode intra-prediction mode information of thecurrent block. When among the neighboring blocks adjacent to the currentblock there is an absent neighboring block which is not available for anintra-prediction mode, the prediction mode encoder is configured toencode the intra-prediction mode information of the current block byexcluding the intra-prediction mode using a pixel of the absentneighboring block from a candidate mode group.

Some embodiments of the present disclosure provide a video encodingapparatus including an intra-prediction encoder and a prediction modeencoder. The intra-prediction encoder is configured to intra-predictionencode subblocks of a current block by using pixels of neighboringblocks adjacent to the subblocks. The prediction mode encoder isconfigured to encode intra-prediction mode information of the currentblock. The intra-prediction mode information includes a prediction modesingle coding flag indicating whether predicted values ofintra-prediction modes of at least a preset number of subblocks in thecurrent block are matched with actual intra-prediction modes or not.

Some embodiments of the present disclosure provide a video decodingapparatus including a prediction mode decoder and an intra-predictiondecoder. The prediction mode decoder is configured to exclude, whenamong neighboring blocks adjacent to a current block there is an absentneighboring block which is not available for an intra-prediction mode,the intra-prediction mode using a pixel of the absent neighboring blockfrom a candidate mode group so as to reconstruct information on one ormore intra-prediction modes of the current block from a bitstream. Theintra-prediction decoder is configured to generate a predicted block ofthe current block, by using the reconstructed one or moreintra-prediction modes, for reconstructing the current block.

Some embodiments of the present disclosure provide a video decodingapparatus including a prediction mode decoder and an intra-predictiondecoder. The prediction mode decoder is configured to decode informationon intra-prediction modes of subblocks of a current block to bereconstructed from a bitstream, and to reconstruct the intra-predictionmodes based on a prediction mode single coding flag included in theinformation on the intra-prediction modes. The single coding flagindicates whether the predicted values of the intra-prediction modes ofat least a preset number of subblocks are matched with actualintra-prediction modes or not. The intra-prediction decoder isconfigured to generate a predicted block of the current block, by usingthe reconstructed intra-prediction modes, for reconstructing the currentblock.

Some embodiments of the present disclosure provide a video decodingmethod performed by a video decoding apparatus. In the video decodingmethod, when among neighboring blocks adjacent to a current block thereis an absent neighboring block which is not available for anintra-prediction mode, the intra-prediction mode using a pixel of theabsent neighboring block is excluded from a candidate mode group so asto reconstruct information on one or more intra-prediction modes of thecurrent block from a bitstream. The video decoding method furtherincludes generating a predicted block of the current block by using thereconstructed one or more intra-prediction modes, and reconstructing thecurrent block by using the predicted block.

Some embodiments of the present disclosure provide a video decodingmethod performed by a video decoding apparatus. In the video decodingmethod, information on intra-prediction modes of subblocks of a currentblock to be reconstructed is decoded from a bitstream. Theintra-prediction modes are constructed based on a prediction mode singlecoding flag included in the information on the intra-prediction modes.The single coding flag indicates whether predicted values of theintra-prediction modes of at least a preset number of subblocks arematched with actual intra-prediction modes or not. The video decodingmethod further includes generating a predicted block of the currentblock by using the reconstructed intra-prediction modes, andreconstructing the current block by using the predicted block.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic block diagram of a video encoding apparatusaccording to at least one embodiment of the present disclosure;

FIG. 2 is an exemplary diagram of an intra 4×4 prediction mode ofH.264/AVC;

FIG. 3 is an exemplary diagram of a usable intra prediction mode and anunusable intra prediction mode of a block located at a picture boundary;

FIG. 4 is a schematic block diagram of a configuration of a videodecoding apparatus according to at least one embodiment of the presentdisclosure;

FIG. 5 is a diagram of an example where neighboring blocks used forpredicting a current block have the nearly same pixel values;

FIG. 6 is a diagram of an exemplary table referred to by a predictionmode encoder when the encoder generates information on the number ofsubblocks of which most probable modes (MPMs) are matched with actualintra-prediction modes.

FIG. 7 is an exemplary diagram illustrating whether prediction modes ofsome subblocks match with MPMs or not within a macroblock in an intra4×4 prediction;

FIG. 8 is another exemplary diagram illustrating whether predictionmodes of some subblocks match with MPMs or not within a macroblock in anintra 4×4 prediction;

FIG. 9 is an exemplary diagram of a table for binarizing the positionsof 4×4 subblocks; and

FIG. 10 is yet another exemplary diagram illustrating whether predictionmodes of some subblocks match with MPMs or not within a macroblock in anintra 4×4 prediction.

DETAILED DESCRIPTION

Some embodiments of the present disclosure improve a coding efficiencyin a video encoding or decoding by reducing unnecessary or overlappinginformation included in intra-prediction mode information when the intraprediction mode information is encoded.

Hereinafter, a video encoding apparatus and a video decoding apparatusdescribed below may be user terminals such as a personal computer (PC),a notebook computer, personal digital assistant (PDA), portablemultimedia player (PMP), PlayStation Portable (PSP), wirelesscommunication terminal, smart phone, TV and the like, or serverterminals such as an application server, service server and the like,and may refer to various apparatuses including (i) a communicationapparatus such as a communication modem and the like for performingcommunication with various types of devices or a wired/wirelesscommunication network, (ii) a memory for storing various types ofprograms and data for encoding or decoding a video or performing aninter or intra prediction for the encoding or decoding, and (iii) amicroprocessor and the like for executing the program to perform anoperation and control. According to one or more embodiments, the memorycomprises a computer-readable recording/storage medium such as a randomaccess memory (RAM), a read only memory (ROM), a flash memory, anoptical disk, a magnetic disk, a solid-state disk, and the like.According to one or more embodiments, the microprocessor is programmedfor performing one or more of operations and/or functionality describedherein. According to one or more embodiments, the microprocessor isimplemented, in whole or in part, by specifically configured hardware(e.g., by one or more application specific integrated circuits orASIC(s)).

Further, a video encoded into a bitstream by the video encodingapparatus may be transmitted in real time or non-real-time to the videodecoding apparatus through wired/wireless communication networks such asthe Internet, wireless personal area network (WPAN), wireless local areanetwork (WLAN), WiBro (wireless broadband, aka WiMax) network, mobilecommunication network and the like or through various communicationinterfaces such as a cable, a universal serial bus (USB) and the like,and thus decoded in the video decoding apparatus and reconstructed andreproduced as the video.

A video typically may include a series of pictures (also referred toherein as “images” or “frames”) each of which is divided intopredetermined areas, such as blocks. When a frame of the video ispartitioned into blocks, the partitioned blocks may be classified intoan intra block or an inter block depending on an encoding method. Theintra block means a block that is encoded through an intra predictioncoding method which generates a predicted block by predicting a pixel ofa current block using pixels of a reconstructed block that underwentprevious encoding and decoding and then encodes a differential valuebetween the predicted block and the pixel of the current block within acurrent picture (i.e., current frame) where the current encoding isperformed. The inter block means a block that is encoded through aninter prediction encoding which generates the predicted block bypredicting the current block in the current picture through referencingone or more past pictures or future pictures and then encoding thedifferential value of the predicted block from the current block. Here,the picture that is referenced in encoding or decoding the currentpicture is called a reference picture (or reference frame).

FIG. 1 is a block diagram schematically illustrating a video encodingapparatus 100 according to at least one embodiment of the presentdisclosure.

The video encoding apparatus 100 according to at least one embodiment ofthe present disclosure is an apparatus for encoding a video and mayinclude an intra-prediction encoder and a prediction mode encoder 182.The intra-prediction encoder according to the present disclosure mayinclude a prediction unit 110, a subtractor 120, a transforming unit130, a quantizing unit 140, dequantizing unit 150, an inversetransforming unit 160, an adder 170, a bitstream generator 180, adeblocking filter 190, and a memory 192, and some of the above-listedcomponents may not be included, or some or all of the components may beselectively included according to the implementation.

A video to be encoded is input in units of blocks, and the block mayhave an m×n form in the present disclosure, wherein m and n have varioussizes and m and n are the same or different.

The prediction unit 110 generates a predicted block by predicting atarget block to be currently encoded in a video by using anintra-prediction or inter-prediction scheme. That is, when theprediction unit 110 performs the intra-prediction, the prediction unit110 generates the predicted block having a predicted pixel value of eachpixel predicted by predicting a pixel value of each pixel of the targetblock to be encoded in the video based on a determined optimalprediction mode. Here, a prediction mode having the smallest encodingcost may be determined as the optimal prediction mode among variousintra-prediction modes for the intra-prediction (for example, nineprediction modes in each of an intra 8×8 prediction and an intra 4×4prediction and four prediction modes in an intra 16×16 prediction inH.264/AVC).

FIG. 2 is diagram illustrating an example of an intra 4×4 predictionmode of H.264/AVC. Referring to FIG. 2, the intra 4×4 predictionincludes nine prediction modes, such as a vertical mode, a horizontalmode, a Direct Current (DC) mode, a diagonal down-left mode, a diagonaldown-right mode, a vertical-right mode, a horizontal-down mode, avertical-left mode, and a horizontal-up mode. The prediction unit 110can calculate an encoding cost of each prediction mode according to ablock mode or a block size of the target block and determine theprediction mode having the smallest encoding cost as the optimalintra-prediction mode.

The subtractor 120 generates a residual block by subtracting thepredicted block from the target block to be encoded (that is, currentblock). That is, the subtractor 120 generates the residual blockincluding a residual signal in a block form by calculating a differencebetween the pixel value of each pixel of the target block to be encodedand the predicted pixel value of each pixel of the predicted blockpredicted by the prediction unit 110.

The transforming unit 130 transforms each pixel value of the residualblock to a frequency coefficient by transforming the residual block to afrequency domain. Here, the transforming unit 130 can transform theresidual signal to the frequency domain by using various transformschemes which transform an image signal on a spatial axis to a componenton a frequency axis, such as a Hadamard transform, a discrete cosinetransform (DCT) based transform and the like, and the residual signaltransformed to the frequency domain becomes the frequency coefficient.

The quantizing unit 140 quantizes the frequency coefficient which isgenerated by transforming the residual block to the frequency domain bythe transforming unit 130. Here, the quantizing unit 140 can quantizethe transformed residual block by using a Dead Zone Uniform ThresholdQuantization (hereinafter, referred to as “DZUTQ”), a quantizationweighted matrix, an improved quantization scheme thereof or the like.

The bitstream generator 180 outputs a bitstream by encoding a quantizedfrequency coefficient stream by using an entropy-coding scheme or thelike. An entropy encoding technology may be used as the codingtechnology, but the present disclosure is not limited thereto and canuse various coding technologies.

In addition, the bitstream generator 180 can insert not only thebitstream encoded from the quantized frequency coefficients but alsovarious pieces of information required for decoding the encodedbitstream into encoded data. That is, the encoded data may include acoded block pattern (CBP), a delta quantization parameter, a bitstreamgenerated by encoding the quantized frequency coefficient, a bitstreamfor information required for the prediction and the like.

The dequantizing unit 150 inversely quantizes or dequantizes thefrequency transform block quantized by the quantizing unit 140. That is,the dequantizing unit 150 generates the residual block having thefrequency coefficient by dequantizing the quantized frequencycoefficients of the quantized residual block.

The inverse transforming unit 160 inversely transforms the residualblock dequantized by the inverse quantizing unit 150. Specifically, theinverse transforming unit 160 generates the residual block having thepixel value, that is, the reconstructed residual block by inverselytransforming the frequency coefficients of the dequantized residualblock. Here, the inverse transforming unit 160 can perform the inversetransform by inversely performing the transform scheme used by thetransforming unit 130.

The adder 170 reconstructs the current block, that is the target blockby adding the predicted block predicted by the prediction unit 110 andthe residual block reconstructed by the inverse transforming unit 160.The reconstructed target block passes through the deblocking filter 190.The deblocking filter 190 removes block distortion and like bydeblocking-filtering the reconstructed current block, and the memory 192stores the deblocking-filtered current block so that the current blockcan be used as a reference picture when a next block of the target blockis encoded or another block is encoded in the future.

The prediction mode encoder 182 encodes information on theintra-prediction mode. The prediction mode encoder 182 may beimplemented as a module separated from the bitstream generator 180, orcombined with the bitstream generator 180 to be implemented as onemodule.

FIG. 3 is diagram illustrating an example of a usable intra-predictionmode and an unusable intra-prediction mode of a block located at apicture boundary. In FIG. 3, a bold unbroken straight line indicates apicture boundary, and a dotted straight line indicates a block boundary.Since a left block and an upper left block of the current block locatedat the picture boundary are not available and cannot be used for theintra-prediction, an unbroken arrow indicates a usable prediction mode,and a dotted arrow indicates an unusable prediction mode.

The current block is predicted by using pixels of neighboring blocks ofthe current block. When some prediction modes find no correspondingneighboring blocks or find unusable neighboring blocks, theintra-prediction mode in the corresponding directions cannot be used. Inthis case, generating intra-prediction mode information with thecorresponding prediction mode inserted into a candidate mode groupresults in adding an unnecessary bit.

When, among the neighboring blocks adjacent to the current block, thereis an absent neighboring block which is not available or cannot be usedfor an intra-prediction mode, the prediction mode encoder 182 can encodeinformation on the intra-prediction mode (or intra-prediction modeinformation) of the current block by excluding the intra-prediction modeusing a pixel of the absent neighboring block from a candidate modegroup, i.e., a group of intra-prediction modes to be included in theencoded intra-prediction mode information of the current block. In otherwords, the prediction mode encoder 182 does not encode information onthe intra-prediction mode(s) using pixel(s) of the absent neighboringblock(s). In particular, since the current block to be encoded islocated at the picture boundary as illustrated in FIG. 3, when there isa neighboring block which does not exist (that is, an absent neighboringblock, for example, the left block and the upper left block in FIG. 3)or there is a block which cannot be used for the intra-prediction amongthe neighboring blocks as described above, the intra-prediction mode inthe corresponding direction cannot be used. In FIG. 3, there are no leftblock and upper left block of the current block, and therefore only thevertical mode, the diagonal down-left mode, the vertical-left mode andthe DC mode can be used, whereas the horizontal mode, the diagonaldown-right mode, the vertical-right mode, the horizontal-down mode andthe horizontal-up mode cannot be used. However, generating theintra-prediction mode information with even the unusable predictionmodes included in the candidate mode group will cause unnecessary extrabits added to the intra-prediction mode information.

Accordingly, in the case of FIG. 3, the prediction mode encoder 182 cantake just four usable prediction modes in generating theintra-prediction mode information, enabling the intra-prediction modesto be encoded by using fewer bits. Then, the neighboring blocks arechecked for their status, and if the presence of at least one unusableprediction mode is confirmed, the corresponding prediction modes areexcluded (but maintaining the remaining usable prediction modes) fromthe candidate mode group for generating the intra-prediction modeinformation, whereby improving the encoding efficiency. For example, insuch codec scheme as H.264/AVC, the prediction mode of the current blockis predicted by using modes of the left block and the upper block. Atthis time, the encoding is performed by using 1 bit when a predictedvalue is matched with an actual predicted mode, and performed by using 4bits when the predicted value is not matched with the actual predictedmode. However, in the case of FIG. 3, when the prediction mode of thecurrent block is predicted by using modes of the left block and theupper block according to the present disclosure, the encoding isperformed by using 1 bit when the predicted value is matched with theactual prediction mode, and performed by using only 3 bits when thepredicted value is not matched with the actual predicted mode, andtherefore the encoding efficiency can be increased. The presentembodiment is an example with H.264/AVC, but the present disclosure isnot limited to this event of the prediction mode set as present inH.264/AVC.

FIG. 4 is a block diagram for schematically illustrating a configurationof a video decoding apparatus 400 according to at least one embodimentof the present disclosure.

The video decoding apparatus 400 according to at least one embodiment ofthe present disclosure includes an intra-prediction decoder and aprediction mode decoder 440. Here, the intra-prediction decoderaccording to the present disclosure may include a bitstream decoder 410,a dequantizing unit 420, an inverse transforming unit 430, a predictionunit 450, an adder 460, a deblocking filter 470, and a memory 480, andsome of the above-listed components may not be included, or some or allof the components may be selectively included according to theimplementation.

The video decoding apparatus 400 may include the bitstream decoder 410,the dequantizing unit 420, the inverse transforming unit 430, aprediction mode decoder 440, the prediction unit 450, the adder 460, thedeblocking filter 470, and the memory 480. Meanwhile, theintra-prediction decoder according to the present disclosure may includethe bitstream decoder 410, the dequantizing unit 420, the inversetransforming unit 430, the prediction unit 450, the adder 460, thedeblocking filter 470, and the memory 480.

The bitstream decoder 410 can generate a block having a quantizedfrequency coefficient by extracting a quantized frequency coefficientstream by decoding a bitstream and inversely scanning the quantizedfrequency coefficient stream.

The dequantizing unit 420 reconstructs a frequency coefficient block bydequantizing the quantized frequency coefficient decoded by thebitstream decoder 410.

The inverse transforming unit 430 reconstructs a residual block byinversely transforming the frequency coefficient block reconstructed bythe dequantizing unit 420.

Since the dequantizing unit 420 and the inverse transforming unit 430perform the same or similar functions to those of the dequantizing unit150 and the inverse transforming unit 160 described through FIG. 1,respectively, detailed descriptions thereof will be omitted.

The prediction mode decoder 440 decodes information on theintra-prediction mode from the bitstream. The prediction mode decoder440 may be implemented as a module separated from the bitstream decoder410, or may be combined with the bitstream decoder 410 to be implementedas one module.

The prediction unit 450 generates a predicted block by using pixels ofneighboring blocks adjacent to the current block and information on theintra-prediction mode extracted from the prediction mode decoder 440.

The adder 460 reconstructs a target block by adding the predicted blockgenerated by the prediction unit 450 and the residual blockreconstructed by the inverse transforming unit 430. The reconstructedtarget block is deblocking-filtered by the deblocking filter 470 andthen stored in the memory 480, and can be used as a reference picturewhen a next block of the target block is reconstructed or another blockis reconstructed in the future.

Meanwhile, when there is an absent neighboring block which cannot beused for the intra-prediction among neighboring blocks including pixelsused for the intra-prediction mode, the prediction mode decoder 440 candecode information on the intra-prediction mode from the bitstream byexcluding the intra-prediction mode using pixels of the absentneighboring block from the candidate mode group. In other words, asillustrated in FIG. 3, when only four intra-prediction modes areavailable for use, for example, in a case of the codec such asH.264/AVC, the prediction mode decoder 440 decodes one bit informationfor indicating whether a predicted MPM (Most Probable Mode) that is theintra-prediction mode of the current block determined fromintra-prediction modes of the neighboring blocks matches or unmatcheswith an actual intra-prediction mode, wherein the MPM is predicted as anintra-prediction mode which has a lowest intra-prediction mode valueamong intra-prediction modes of the neighboring blocks of the currentblock. When the one-bit information indicates that the MPM is matchedwith the actual prediction mode, the intra-prediction mode of thecurrent block is determined from the intra-prediction modes of theneighboring blocks. In the case where the one-bit information indicatesthat the MPM is not matched with the actual prediction mode, e.g., whenthe current block is located in the position as illustrated in FIG. 3,the intra-prediction mode can be reconstructed among currently availableintra-prediction modes by identifying that only four intra-predictionmodes (including the DC mode) can be used and decoding only 3 bits fromthe bitstream with the intra-prediction mode.

FIG. 5 is a diagram illustrating an example where neighboring blocksused for predicting a current block have nearly the same pixel values.

In the video encoding apparatus 100 according to at least one embodimentof the present disclosure, the prediction mode encoder 182 can encodeinformation on the intra-prediction mode of the current block byunifying all intra-prediction modes using only pixels having similarvalues among pixels used for the intra-prediction mode and inserting theunified mode into a candidate mode group.

When pixel values of the neighboring blocks used for predicting thecurrent block have similar values, information on the intra-predictionmode can be reduced, thereby increasing an encoding efficiency. Forexample, as illustrated in FIG. 5, when z1 to z9 are configured to havenearly the same value (or the same value), since predicted blocksgenerated by using intra-prediction modes after using pixels of an upperleft block, an upper block and an upper right block of the current blockmay have predicted signals of nearly the same value, theintra-prediction modes have overlapping prediction mode characteristics.Accordingly, by inserting only one of the prediction modes predictedfrom the pixels of the neighboring blocks having nearly the same valueinto a candidate mode group, the possible redundancy in predicting theprediction of the intra-prediction mode information can be removed.

Accordingly, in a case of FIG. 5, the vertical mode, the diagonal-leftmode, the vertical-left mode and the like have similar predictedresults, so that they can be unified and represented as one mode. Inother words, seven modes, not nine modes, can be encoded as thecandidate mode group.

Here, whether the pixel values of the neighboring blocks used forpredicting the current block have the similar (or nearly the same)values may be determined based on at least one neighboring blocksimilarity from the similarity between neighboring pixels of the leftblock of the current block, the similarity between neighboring pixels ofthe left block, upper left block and upper block of the current block,the similarity between neighboring pixels of the upper block and upperright block of the current block and the like, but the presentdisclosure is not limited thereto. Here, the similarity/nonsimilaritydetermination is achieved by using a statistical average characteristicof the adjacent pixels, for example, by determining whether a variancevalue of the adjacent pixels is equal to or smaller than a predeterminedvalue, but the inter pixel similarity/nonsimilarity determination is notlimited to the method using the variance and may use various methodsincluding a method of determining equal or smaller inter pixeldifferences than a predetermined value.

For example, when it is determined that there is the similarity amongadjacent pixels (a to d, z1 to z4 and z9) of the left block, upper leftblock and upper block of the current block, a mode unification can beperformed on the vertical mode, horizontal mode, diagonal-right mode,vertical-right mode, horizontal-down mode, horizontal-up mode and thelike and the unified mode can be inserted into the candidate group ofthe prediction mode to be encoded. Accordingly, the encoding isperformed only with the four modes including the DC mode, diagonal-leftmode, vertical-left mode and unified mode, thereby reducing the numberof encoding bits of the intra-prediction mode.

As stated above, when such codec scheme as H.264/AVC predicts theprediction mode of the current block by using the prediction modes ofthe left block and the upper block of the current block, the encoding isperformed by using 1 bit when the predicted value is matched with theactual prediction mode, and performed by using 4 bits when the predictedvalue is not matched with the actual prediction mode. However, in thepresent disclosure, the prediction mode of the current block ispredicted by using modes of the left block and the upper block, and theencoding is performed by using 1 bit when the predicted value is matchedwith the actual prediction mode and performed by totally using only 3bits (2 bits of which are for encoding the four modes) when thepredicted value does not match the actual prediction mode, therebyincreasing the encoding efficiency.

As described above, when the prediction mode encoder 182 encodesinformation on the intra-prediction mode of the current block byunifying all intra-prediction modes using only pixels having similarvalues among pixels used for the intra-prediction modes and insertingthe combined one mode into the candidate mode group, the prediction modedecoder 440 of the video decoding apparatus 400 can reconstruct theintra-prediction mode by the number of required bits from the bitstreamby unifying all intra-prediction modes using only pixels having similarvalues among pixels used for the intra-prediction modes throughidentification of pixel values of the neighboring blocks and insertingthe unified mode into the candidate mode group.

Meanwhile, the prediction mode encoder 182 can encode intra-predictionmode information including a prediction mode single coding flag whichindicates whether the prediction values of intra-prediction modes of atleast a preset number of subblocks within the target block to encode arematched with actual intra-prediction modes.

As described above, when there are more cases of predicting theintra-prediction modes of the current block to match the actualintra-prediction mode, the encoding efficiency can be increased. Forexample, in H.264/AVC, the encoding is performed by using one bit whenpredicting the intra-prediction mode of the current block by usingprediction modes of the upper block and the left block of the currentblock to match the actual intra-prediction mode, and the encoding isperformed by using four bits when the predicted intra-prediction mode isnot matched with the actual intra-prediction mode.

It is assumed that there are M subblocks within the target block andthere are N cases (i.e., subblocks) where the mode of the current blockpredicted using intra-prediction modes of the neighboring blocks ismatched with the actual intra-prediction mode. When A is the number ofbits used when the predicted intra-prediction mode of the current blockis matched with the actual intra-prediction mode and B is the number ofbits used when the predicted intra-prediction mode of the current blockis not matched with the actual intra-prediction mode, N*A+(M−N)*B bitsare used for the intra-prediction mode information in the current block.As N increases and thus approaches M, a smaller number of bits is usedfor the intra-prediction mode information of the current block. However,as N increases, overlapping bits are increasingly included. When N is M,M (or N) bits are used (assuming A is 1) for encoding theintra-prediction mode information. For example, in H.264/AVC and in caseof the intra 4×4, when the prediction is accurately performed on allintra-prediction modes of sixteen subblocks (M=16), sixteen bits areused for the intra-prediction mode information of the current block.

Accordingly, the present disclosure provides a method of transmittingpieces of intra-prediction mode information en bloc in order to removeredundancy of intra-prediction mode information predicted in the targetblock. As a result of predicting intra-prediction modes of the presetnumber (or more) of subblocks among M subblocks within the target blockby using left block and upper block thereof, when the predictedintra-prediction mode is identical to the actual intra-prediction mode,intra-prediction mode information including the prediction mode singlecoding flag is transmitted, instead of transmitting the intra-predictionmode information to every subblock. The prediction mode single codingflag indicates whether the preset number (or more) of blocks among the Msubblocks within the target block are matched with the actual modes.

Along with the prediction mode single coding flag, included in theintra-prediction mode information to be encoded are information of thenumber and positions of subblocks of which predicted values ofintra-prediction modes are not matched with actual intra-predictionmodes as well as information on the actual intra-prediction mode, andthereby the intra-prediction mode information can be reduced and theencoding can be efficiently performed. As a result of predictingintra-prediction modes of the M subblocks, when there are smaller thanpreset number of cases where the predicted intra-prediction mode ismatched with the actual intra-prediction mode, encoding is performed ona prediction mode single coding flag which indicates encoding by theconventional method (that is, encoding the intra-prediction mode foreach subblock).

Particularly, when a quantization parameter is large (that is, at a lowbit rate), a ratio of the intra-prediction mode information to totallygenerated bits is high. Accordingly, by reducing overlapping intraprediction mode information, the high encoding efficiency can beobtained.

As described above, when the prediction mode encoder 182 encodes theintra-prediction mode information including the prediction mode singlecoding flag indicating whether the predicted values of theintra-prediction modes of at least the preset number of subblocks withinthe target blocks to encode are matched with the actual intra-predictionmode, the prediction mode decoder 440 of the video decoding apparatus400 can decode the intra-prediction mode information of the subblock ofthe current block to be reconstructed from the bitstream and canreconstruct the intra-prediction mode based on whether the predictionmode single coding flag included in the intra-prediction modeinformation means to indicate that the predicted value of theintra-prediction mode of the preset number of subblocks is matched withthe actual intra-prediction mode. Here, information on the preset numbermay be mutually agreed between the video encoding apparatus and thevideo decoding apparatus, or may be transmitted by the video encodingapparatus to the video decoding apparatus in units of sequences, slicesof the video or the like.

Accordingly, when the prediction mode single coding flag indicates thatpredicted values of the intra-prediction modes of at least the presetnumber of subblocks are matched with the actual intra-prediction modes,the prediction mode decoder 440 can reconstruct the intra-predictionmodes of all subblocks by decoding the number of subblocks of which thepredicted values of the intra-prediction modes are not matched with theactual intra-prediction modes included in the intra-prediction modeinformation, positions of the subblocks, and information on the actualintra-prediction modes.

Further, when the prediction mode single coding flag indicates that thepredicted values of the intra-prediction modes of at least the presetnumber of subblocks are not matched with the actual intra-predictionmodes, the prediction mode decoder 440 can reconstruct theintra-prediction modes of all subblocks by decoding the intra-predictionmode for each subblock included in the intra-prediction modeinformation.

FIG. 6 is a diagram illustrating an example of a table referred to whenthe prediction mode encoder 182 generates information on the number ofsubblocks of which most probable modes (MPMs) are matched with actualintra-prediction modes.

For example, in case where the intra 4×4 prediction is performed in the16×16 block to generate information on the intra-prediction mode, tohave information on thirteen or more subblocks generated among sixteensubblocks, various methods are used are to allocate bits to each pieceof information. For example, referring to the table of FIG. 6, 0 isgenerated when there are sixteen subblocks of which the MPMs are equal(or matched) to the actual intra-prediction modes, a binarized code “10” is generated when the number of subblocks is fifteen, a binarizedcode “1 1 0” is generated when the number of subblocks is fourteen, anda binarized code “1 1 1” is generated when the number of subblocks isthirteen.

Further, a tree can be used for generating information on the positionsof the subblocks of which the MPMs are not matched with the actualintra-prediction modes, thereby increasing the encoding efficiency.

For example, when sixteen subblocks sized 4×4 are assumed to be presentin a block, also referred to herein as macroblock (MB), sized 16×16,suppose that a preset value of 13 is a reference point for using themethod according to the present disclosure. If the MPMs of 14 subblocksin an MB are matched with the actual prediction modes and the MPMs ofthe remaining 2 subblocks are not matched with the actual predictionmodes in one macroblock, which represents that the 14 subblocks have theMPMs matching with the actual prediction modes, then the presentlydisclosed method involves in encoding the intra-prediction mode. At thistime, information on the position can be binarized and encoded by way oftree-based transmission.

FIG. 7 is a diagram illustrating an example of showing prediction modesof subblocks which are matched with the MPM or not within the macroblockin the intra 4×4 prediction.

With respect to the current block, the prediction mode encoder 182generates information on whether there is an intra-prediction subblockof which the MPM is not matched with the actual prediction mode in fourlower level (i.e., first order) subblocks having a ½ size of the currentblock by both length and width. With respect to lower level (i.e., firstorder) subblocks also, if second order subblocks having a ¼ size of thecurrent block (in both length and width) are larger than theintra-prediction unit (i.e., 4×4), information is generated in a quadtree form for sequentially indicating whether the second order subblockshave an intra-prediction subblock of which the MPM is not matched withthe actual prediction mode.

As illustrated in FIG. 7 at A, when the MPM is not matched with theactual prediction mode at two (second order) subblock positions (markedX), information on the corresponding subblocks is generated. When thetree (for example, quad tree) is used, the macroblock (16×16) is dividedinto four first order subblocks (8×8) each having a ½ size of thecorresponding macroblock in both the length and width. In a raster scanorder, 1 is allocated to a first order subblock with a second ordersubblock (4×4) of which the MPM is not matched with the actualprediction mode as illustrated in FIG. 7 at B. To a first order subblockwith no second order subblock of which the MPM is not matched with theactual prediction mode (marked 0), 0 is allocated (allocations of 0 and1 may be inversely performed in at least one embodiment). In this way,binary information “1 1 0 0” is generated, for example.

Since the prediction mode encoder 182 generates information on thenumber of subblocks of which the MPMs are not matched with the actualprediction modes with reference to the table of FIG. 6, it can be knownthrough binary information of “1 1 0 0” generated in the case of FIG. 7that the number of subblocks of which the MPMs are not matched with theactual prediction modes in each of the 8×8 blocks indicated by 1 is one.Accordingly, in the 8×8 block having the value of 1, information on theposition of the one 4×4 block of which the MPM is not matched with theactual prediction mode within the 8×8 block can be generated byadditionally using two bits. In FIGS. 7A and 7B, position information ofa total of eight bits is generated. The eight bits are generated byadding four bits, each bit being allocated to each of the 8×8 blocks,and position information of four bits, each two bits being allocated tothe 4×4 block within the 8×8 block of which the MPM is not matched withthe actual prediction mode. The number of bits is equal to the number ofbits in the case where information on two positions of the 4×4 blockswithin the 16×16 block is transmitted. As illustrated in FIGS. 7A and7B, when MPMs of fourteen subblocks are matched with the actualprediction modes, MPMs of two subblocks are not matched with the actualprediction modes. Accordingly, when MPMs of a first 8×8 block and asecond 8×8 block are not matched with the actual prediction modes, thebinary information of “1 1 0 0” can be reduced to binary information of“1 1” (since information indicating that MPMs of only two subblocks arenot matched with the actual prediction modes can be known in advance asillustrated in FIG. 6, when the first and second 8×8 blocks correspondto a binary code “1 1”, third and fourth 8×8 blocks naturally correspondto a binary code “0 0”, thereby omitting two bits “0 0”).

FIG. 8 is a diagram for showing another example illustrating predictionmodes of subblocks which are matched with the MPM or not within themacroblock in the intra 4×4 prediction.

As illustrated in FIG. 8 at A, in the case where there are 4×4 subblocksof which MPMs are matched with actual prediction modes within themacroblock in the intra 4×4 prediction, when information on blocks ofwhich MPMs are not matched with intra 4×4 prediction mode information isgenerated in units of 8×8 blocks by using the quad tree in the same wayused in FIG. 7, binary information of “1 0 0 0” is generated asillustrated in FIG. 8 at B. It means that positions of two 4×4 subblocksof which the MPMs are not matched with the actual prediction modes areincluded in one 8×8 block. Accordingly, in the first 8×8 block, positioninformation of the 4×4 subblock of which the MPM is not matched with theactual prediction mode is generated by using two bits. And then, in thesame 8×8 block, position information of the other 4×4 subblock of whichthe MPM is not matched with the actual prediction mode is transmitted byusing two bits.

A position of each subblock can be binarized. For example, FIG. 9 is adiagram illustrating an example of a table in which positions of 4×4subblocks are binarized.

In FIG. 8, one 4×4 subblock (for example, first upper left subblock) ofwhich the MPM is not matched with the actual prediction mode can bepresented by position information using two bits, and there remains acandidate group including three 4×4 subblocks in the corresponding 8×8block except for the upper left subblock. Accordingly, positioninformation of the remaining (second) subblock of which the MPM is notmatched with the actual prediction mode may be binarized as illustratedin FIG. 9.

That is, as illustrated in FIG. 9, when the other (second) 4×4 subblockof which the MPM is not matched with the actual prediction modecorresponds to an upper right 4×4 subblock, only one bit of “0” istransmitted instead of the conventional two bits, so that the number ofbits required for encoding position information of the other subblock ofwhich the MPM is not matched with the actual prediction mode can bereduced.

FIG. 10 is a diagram illustrating still another example of showingprediction modes of subblocks which are matched with MPMs or not withinthe macroblock in the intra 4×4 prediction.

In the case where a size of a lower level (e.g., second order) subblockis equal to an intra-prediction unit, only information of a position ofthe subblock of which the MPM is not matched with the actual predictionmode is generated when there is one piece of information indicating thatthe MPM is not matched with the actual prediction mode, and onlyinformation on a position of the subblock of which the MPM is matchedwith the actual prediction mode is generated when there are three piecesof information indicating the MPM is not matched with the actualprediction mode.

For example, when thirteen MPMs are matched with actual predictionmodes, preset thirteen or more MPMs are matched with actual predictionmodes, and therefore the intra-prediction modes can be encoded by usingthe suggested method.

As illustrated in FIG. 10 at A, when the MPM is matched with the actualprediction mode, binary bits of “1 0 0 0” can be generated in a quadtree form as illustrated in FIG. 10 at B.

In FIG. 10, there are three 4×4 subblocks of which MPMs are not matchedwith actual prediction modes. Through binary information of “1 0 0 0”indicated by the quad tree, it can be known that there are three 4×4subblocks of which MPMs are not matched with actual prediction modes ina first 8×8 block. In this case, since it is known in advance that MPMsof thirteen subblocks are matched with the actual prediction modes, MPMsof the subblocks within the macroblock which are matched with the actualprediction modes can be identified with six bits generated by addingfour bits (i.e., “1 0 0 0”) and two bits of position information of theone 4×4 subblock of which the MPM is matched with the actual predictionmode within the first 8×8 block to the quad tree, which providesefficiency.

Meanwhile, in the description of the quad tree according to at least oneembodiment, the position information of the subblock of the 4×4 size isgenerated in the block of the 16×16 size, but the present disclosure isnot limited thereto. In generating position information of the subblockof the 4×4 size in the block of the 32×32 size, 4 bit informationindicating whether there is a subblock of the 4×4 size of which the MPMis matched with the actual prediction mode within a sub-area of the16×16 size is generated. And then, with respect to the block (orsub-area) of the 16×16 size in which there is a subblock of the 4×4 sizeof which the MPM is not matched with the actual prediction mode, 4 bitinformation indicating whether there is a subblock of the 4×4 size ofwhich the MPM is matched with the actual prediction mode within thesubarea having the 8×8 size is generated. In the block having subblocksof which sizes are equal to the intra-prediction unit, the positioninformation is not generated with the quad tree any more, butinformation on the position of the subblock (subblock of theintra-prediction unit) of which the MPM is not matched with the actualprediction mode is generated by using a table of FIG. 9. In the aboveexample, although only the subblock of the 4×4 size has been described,the intra-prediction unit size may be set as various sizes as well asthe 4×4 size.

As described above, when the prediction mode encoder 182 generatesinformation on the actual intra-prediction mode in a quad tree form soas to encode the intra-prediction mode, the prediction mode decoder 440of the video decoding apparatus 400 can extract the information on theintra-prediction mode by inversely using the method through which theprediction mode encoder 182 generates the information on the actualintra-prediction mode in the quad tree form from the bitstream. Forexample, if is assumed that the bitstream is encoded by performing the4×4 intra-prediction and a size of the macroblock is 16×16, when abinarized code “1 1 0” is extracted from the bitstream as information onthe number of subblocks of which MPMs are matched with the actualprediction modes (referred to as matching subblocks), the number 14(fourteen) of matching subblocks is decoded by using the table of FIG.6. Accordingly, it can be known that the number of subblocks(non-matching subblocks) of which MPMs are not matched with the actualprediction modes is two. Further, when a binarized code “1 0 0 0” isfurther decoded from the bitstream as information on positions of thenon-matching subblocks, it can be known that the upper left 8×8 subblockof the 16×16 block includes the non-matching subblocks. In addition,when a binarized code “0 0” is further decoded from the bitstream, aposition of a first non-matching subblock can be known through decodedinformation (when it is arranged to perform the encoding clockwise withrespect to the position of the upper left subblock in an order ofbinarized codes “0 0”, “0 1”, “1 0”, and “1 1”, it is known that thedecoded binarized code “0 0” means that the position of the firstnon-matching subblock corresponds to the upper left 4×4 subblock withinan 8×8 upper left block setoff the 16×16 macroblock). Further, in thecase where the further decoded information from the bitstream is “0”,when it is arranged with the video encoding apparatus to use a binarytable of FIG. 9 for information on the position of the secondnon-matching 4×4 subblock, it can be known that the position of thesecond non-matching 4×4 subblock corresponds to the upper right 4×4subblock within the upper left 8×8 block as illustrated in FIG. 8.

Further, in the case where information on the actual intra-predictionmode is reconstructed by using the quad tree, when the number of cases(e.g., 4×4 subblocks) where the MPM is not matched with the actualprediction mode in the lowest level block (e.g., first order block of8×8) is one or three, information on positions of subblocks of whichMPMs are not matched with actual prediction modes can be reconstructedfrom the bitstream by using 1 bit information.

The video encoding/decoding apparatus according to at least oneembodiment of the present disclosure can be implemented by connecting abitstream output terminal of the video encoding apparatus of FIG. 1 to abitstream input terminal of the video decoding apparatus 400 of FIG. 4.

The video encoding/decoding apparatus according to at least oneembodiment of the present disclosure includes a video encoder forencoding a current block by intra-predicting the current block by usingpixels of neighboring blocks adjacent to the current block and encodingan intra-prediction mode of the current block by excluding informationon overlapping or unnecessary intra-prediction modes among all intraprediction modes from a candidate mode group or based on whetherpredicted values of intra-prediction modes of at least a preset numberof subblocks are matched with actual intra-prediction modes, and a videodecoder for reconstructing the intra prediction mode of the currentblock by excluding the overlapping or unnecessary intra-prediction modesamong all the intra prediction modes from the candidate mode group andbased on whether the predicted values of the intra-prediction modes ofthe preset number of subblocks are matched with the actualintra-prediction modes, generating a predicted block of the currentblock to be reconstructed by using a reconstructed intra-predictionmode, and reconstructing the current block.

Here, the video encoder can be implemented by the video encodingapparatus 100 according to at least one embodiment of the presentdisclosure, and the video decoder can be implemented by the videodecoding apparatus 400 according to at least one embodiment of thepresent disclosure.

The video encoding method according to at least one embodiment of thepresent disclosure includes an intra-prediction encoding step S610 ofencoding a current block by intra-predicting the current block by usingpixels of neighboring blocks adjacent to the current block, and aprediction mode encoding step S620 of, when there is an absentneighboring block which cannot be used for the intra-prediction inneighboring blocks including pixels used for an intra-prediction mode,encoding information on an intra-prediction mode of the current block byexcluding an intra-prediction mode using a pixel of the absentneighboring block from a candidate mode group.

The video encoding method according to at least another embodiment ofthe present disclosure includes an intra-prediction encoding step S710of encoding a current block by intra-predicting the current block byusing pixels of neighboring blocks adjacent to the current block, and aprediction mode encoding step S720 of encoding information on anintra-prediction mode of the current block by combining allintra-prediction modes using only pixels having similar values amongpixels used for an intra-prediction mode into one mode and inserting thecombined intra-prediction mode into a candidate mode group.

The video encoding method according to still at least another embodimentof the present disclosure includes an intra-prediction encoding stepS810 of intra-prediction encoding subblocks of a current block by usingpixels of neighboring blocks or subblocks adjacent to the subblocks, anda prediction mode encoding step S820 of encoding information on anintra-prediction mode including a prediction mode single coding flagindicating whether predicted values of intra-prediction modes of atleast a preset number of subblocks are matched with actualintra-prediction modes.

Here, since the intra-prediction encoding steps S610, S710, and S810 maycorrespond to the operation of the intra-prediction encoder and theprediction mode encoding steps S620, S720, and S820 may correspond tothe operation of the prediction mode encoder 182, detailed descriptionsthereof will be omitted.

The video decoding method according to at least one embodiment of thepresent disclosure includes a prediction mode decoding step S910 of,when there is an absent neighboring block which cannot be used for anintra-prediction in neighboring blocks including pixels used for anintra-prediction mode, excluding an intra-prediction mode using a pixelof the absent neighboring block from a candidate mode group so as toreconstruct information on the intra-prediction mode from a bitstream,and an intra-prediction decoding step S920 of generating a predictedblock of a current block to be reconstructed by using a reconstructedintra-prediction mode and reconstructing the current block.

The video decoding method according to at least another embodiment ofthe present disclosure includes a prediction mode decoding step S1010 ofcombining all intra-prediction modes using only pixels having similarvalues among pixels used for an intra-prediction mode into one mode andinserting the combined intra-prediction mode into a candidate mode groupso as to reconstruct the intra-prediction mode from a bitstream, and anintra-prediction decoding step S1020 of generating a predicted block ofa current block to be reconstructed by using a reconstructedintra-prediction mode and reconstructing the current block.

The video decoding method according to still at least another embodimentof the present disclosure includes a prediction mode decoding step S1110of decoding information on an intra-prediction mode of a subblock of acurrent block to be reconstructed from a bitstream and reconstructingthe intra-prediction mode based on a prediction mode single coding flagincluded in the information on the intra-prediction mode indicatingwhether predicted values of intra-prediction modes of at least a presetnumber of subblocks are matched with actual intra-prediction modes, andan intra-prediction decoding step S1120 of generating a predicted blockof the current block to be reconstructed by using a reconstructedintra-prediction mode and reconstructing the current block.

Here, since the prediction mode decoding steps S910, S1010, and S1110and the intra-prediction decoding steps S920, S1020, and S1120 maycorrespond to operations of the prediction mode decoder 440 and theintra-prediction decoder, respectively, detailed descriptions thereofwill be omitted.

The video encoding/decoding method according to at least one embodimentof the present disclosure can be implemented by combining the videoencoding method according to at least one embodiment of the presentdisclosure and the video decoding method according to at least oneembodiment of the present disclosure.

The video encoding/decoding method according to at least one embodimentof the present disclosure includes encoding a current block byintra-predicting the current block by using pixels of neighboring blocksadjacent to the current block and encoding an intra-prediction mode ofthe current block by excluding information on overlapping or unnecessaryintra-prediction modes among all intra prediction modes from a candidatemode group or based on whether predicted values of intra-predictionmodes of at least a preset number of subblocks are matched with actualintra-prediction modes, and reconstructing the intra prediction mode ofthe current block by excluding the overlapping or unnecessaryintra-prediction modes among all the intra prediction modes from thecandidate mode group and based on whether the predicted values of theintra-prediction modes of at least the preset number of subblocks arematched with the actual intra-prediction modes, generating a predictedblock of the current block to be reconstructed by using a reconstructedintra-prediction mode, and reconstructing the current block.

According to some embodiments of the present disclosure as describedabove, in a video encoding or decoding method or apparatus, when thereis an absent neighboring block in encoding intra-prediction modeinformation, the mode information can be efficiently encoded byexcluding an intra-prediction mode using a reference pixel of the absentneighboring block from a candidate mode group.

Further, in encoding the intra-prediction mode information, whenreference pixels of neighboring pixels have similar values, theintra-prediction mode information is generated by unifyingintra-prediction modes with the similar reference pixels into onecombined mode, thereby efficiently encoding the mode information.

Moreover, by encoding the number and/or position of subblocks, of whichMPMs are not equal (or matched) to actual intra-prediction modes, themode information can be efficiently encoded.

Furthermore, by performing a decoding corresponding to the encodingmethod, the decoding can be performed with the corresponding efficiencyto the efficient encoding.

Although exemplary embodiments of the present disclosure have beendescribed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the characteristics of the disclosure.Therefore, exemplary embodiments of the present disclosure have not beendescribed for limiting purposes. Accordingly, the scope of thedisclosure is not to be limited by the above embodiments.

The invention claimed is:
 1. A video encoding apparatus, comprising: anintra-prediction encoder configured to encode a current block byintra-predicting the current block by using pixels of neighboring blocksadjacent to the current block; and a prediction mode encoder configuredto encode intra-prediction mode information of the current block,wherein, when among the neighboring blocks adjacent to the current blockthere is an absent neighboring block which is not available for anintra-prediction mode, the prediction mode encoder is configured toencode the intra-prediction mode information of the current block usinga minimum size of bits required for identifying the intra-predictionmode of the current block among a candidate mode group which includesonly available intra-prediction modes.
 2. A video decoding apparatus,comprising: prediction mode decoder configured to exclude, when amongneighboring blocks adjacent to a current block there is an absentneighboring block which is not available for an intra-prediction mode,the intra-prediction mode using a pixel of the absent neighboring blockfrom a candidate mode group so as to reconstruct information on one ormore intra-prediction modes of the current block from a bitstream,wherein the information on one or more intra-prediction modes is beingrepresented with a minimum size of bits required for identifying theintra-prediction mode of the current block among the candidate modegroup which includes only available intra-prediction modes; and anintra-prediction decoder configured to generate a predicted block of thecurrent block, by using the reconstructed one or more intra-predictionmodes, for reconstructing the current block.
 3. A video decoding method,the method performed by a video decoding apparatus and comprising:excluding, when among neighboring blocks adjacent to a current blockthere is an absent neighboring block which is not available for anintra-prediction mode, the intra-prediction mode using a pixel of theabsent neighboring block from a candidate mode group so as toreconstruct information on one or more intra-prediction modes of thecurrent block from a bitstream, wherein the information on one or moreintra-prediction modes is being represented with a minimum size of bitsrequired for identifying the intra-prediction mode of the current blockamong the candidate mode group which includes only availableintra-prediction modes; generating a predicted block of the currentblock by using the reconstructed one or more intra-prediction modes; andreconstructing the current block by using the predicted block.